Physics .. "Active" tractor weights .. Shifting the C/G ZTR ??

[cttractor]

Well, think about it. Regardless of the approach, we can never have weight any lower than the wheels themselves. The lowest weighting we can apply to a tractor is filled tires, followed by wheel weights in the middle of the wheel. If the weight is low enough and the mower is wide enough, it should be able to handle some rather steep inclines.

I don't know what weights you've mounted from side-to-side on the mower already, or what they look like -- perhaps you could provide a photo or simple sketch. What if you were to do nothing more than increase the weight you've already mounted at that low location? Did you notice any improvement in stability from the weights you've already added? If so, more weight might be all you need to add, as long as the frame can take it. It certainly has the advantage of being simple and requiring absolutely no control system whatsoever.

 

[tmajor]

The 30 pounds of weights, which I placed underneath the rear, were meant to offset some of the weight of the front and put more weight on the rear drive/steering wheels. This worked well enough to keep it from instantaneously turning down hill, when operating across an incline, if the upper wheel broke loose. I could reposition the weights further aft, which would do even more for steering and control.

However, with the tractor being so heavy (1025 pounds), there is a lot of weight on the lower tire. when on an incline. That is kinda hard on the turf.

How about, a center pivoting transverse weight? Would that have any advantage?

The weights placed underneath, are just 2 steel flat bar stock.

 

[aczlan]

Loaded tires and/or wheel weights will do wonders for you.

Aaron Z

 

[cttractor]

If the weight is going to pivot, it means you need some form of way to control it or it will almost assuredly pivot to the downhill side -- exactly where you don't want it. The beauty of Chevy's approach on the Camero was that no control system was needed because the weights were fixed.

As for the weight of your mower, you know far more than I about your machine and how close you are to its limits. I'm sorry I can't be of further help with that.

By the way, with your next post, you'll be a Silver Member -- Congrats!

 

[Reg]

Here is a new concept, I'm mentally working on.

I've got 30 pounds of weight under the rear of my ZTR mower. This helps with traction, however, even the 30 pounds doesn't balance out the weight of the front (deck, castor wheels, etc.). If I'm going down an incline, with a roll, the mower won't turn toward the up-hill side of the roll. Reason being, the up-hill rear drive wheel has very little weight on it. The 30 pounds underneath, and the mower deck, throw the center of gravity of the tractor toward the lower side.

My thoughts are: If there were two, identical, movable weights (left and right), tied together with a cable and run over a pulley, they would move oppositely, up and down with gravity. This, in itself would not change the center of gravity, but still, make it fall toward the lower wheel. But ... if they were guided by tubes, which were placed at an angle (left and right), the center of gravity would shift toward the higher wheel and away from the lower wheel, possibly keeping the center of gravity line more under the center of the tractor.

Let me hear your thoughts.

As described... swinging weight will tend toward the lower wheel, making the situation worse.
If you mean actively operated counter weights ? Yeah, that would be different and could be done.
According to response time it could get caught out of phase with the actual stability needs, boats have this problem.
Some of us have extended back hoes and swung them up the grade when crossing side slopes.
Once in a while I toy with the idea of a 50 or 100 lb weight on a long or telescoping arm mounted on the top of the ROPS and activated to always point up hill.

Then I focus on the task at hand (-:
I must CONCENTRATE on what I am trying to do, or I may become yet another roll over statistic.

 

[tmajor]

By the way, with your next post, you'll be a Silver Member -- Congrats!

I guess, I might as well go for it!:thumbsup: Thanks.

The thing that cars seem to count on for balance is their suspension. I looked at one article about the "Hugger", but didn't notice anything about weights.

@ aczlan
I have thought about wheel weights or loading them, which I am sure would help with the traction issues. I believe, in all reality, the weight of the original mower should have been more evenly distributed, by sliding operator and engine aft. I would guess, on most ZTR's, that 80% of the weight is forward of the drive axle.

 

[tmajor]

Once in a while I toy with the idea of a 50 or 100 lb weight on a long or telescoping arm mounted on the top of the ROPS and activated to always point up hill.

That is kind of the result I was going for. All tractors, which operate on side-hills would benefit from such.

They mow the sides of the dikes, along the river, with hydraulically adjustable cabs on their mowers. Of course, if the hydros go, they are SOL!

Add: This is a pretty strange mower. I believe, I'd be afraid to use it. Watch the video.

 

[BeezFun]

Loaded tires and/or wheel weights will do wonders for you.

Aaron Z

I talked to the dealer about filling ZTR tires. He said it's a really bad idea because it increases the load on the hydraulic wheel motors more than they were designed for. I thought about that for awhile and decided it's probably because ZTRs go at relatively high speeds compared to a tractor and have very small wheel diameters, so that wheel is really spinning. That means the forces required to accelerate and decelerate the wheels are high, which would be hard on the motors. It also changes the CG on an incline and while it seems like it would make the situation better viewed from behind, from the side it's not so clear if it helps or hurts. I would imagine the CG is pretty close to the rear axle but don't know for sure. Adding weight in the wrong place could cause a problem going up a hill as opposed to going across it.

 

[tmajor]

I would imagine the CG is pretty close to the rear axle but don't know for sure.

On some of the smaller ZTRs, it might be back further, due to the light decks. However, on the mowers with welded decks, the CG falls pretty far forward. I can't even pick the front of mine up ... I use a chain hoist. In addition to the mower being heavy in the front, the operator sits ahead of the rear axle. There is a bunch of weight on those front castor wheels.

Here's a picture I took several years ago, before I added any weight. 60 pounds on the back, still didn't let me lift the front!

 

[BeezFun]

How about, a center pivoting transverse weight? Would that have any advantage?

You might want to google harmonic absorbers, or mass dampers, and get some ideas from how they're built. They don't serve the same purpose that you're interested in, but some of the approaches might be useful. Mass dampers are used at the top of skyscrapers to counteract the swaying motion of the building due to wind load. They take several forms, but they're all massive weights (many tons) that are either moved around by hydraulic pistons, or are tied to the superstructure of the building with the equivalent of huge springs. Their purpose is to change the resonant frequency of the building, but the approach used requires doing mechanical things that are similar to what you are trying to accomplish. One of the earlier posters suggested pumping oil between reservoirs, that would be a good example of this type of approach. It is very hard to analyze the dynamic response of things that move like this, I encourage you to be careful in your research that you don't get a very unexpected performance change.